acalculator

How many plywood sheets?

Pick a floor, wall or pitched roof, type its size and choose the sheet size. The plywood calculator gives the area to cover and the sheets to buy with waste, and the cost if you type a price.

Your numbers

Units
Surface
Sheets to buy
14

Sheets of plywood to buy: 14, for 384 ft².

Area to cover
384 ft²
Sheets without waste
12
Roof slope factor
1

Sheets to buy: 14. Sheets of plywood to buy: 14, for 384 ft².

How to calculate

Plywood calculator: how many 4 × 8 ft (or other) sheets of plywood or OSB cover a subfloor, wall or pitched roof deck, with waste and cost.

Example with the default inputs (Surface Floor or wall, Length 24 ft, Width 16 ft, Sheet size 4 × 8 ft, Waste 10%): Sheets of plywood to buy: 14, for 384 ft².

Method: Sheets = length × width × slope factor × (1 + waste ÷ 100) ÷ sheet area, rounded up; slope factor = √(1 + (pitch ÷ 12)²) for a roof, 1 otherwise.

  • Offcuts are reused where they fit, so sheets are counted by area; waste covers what cannot be reused.
  • A roof is measured in plan (from above), overhangs included; the slope factor turns that into the sloped area.
  • Openings are not taken away; subtract them from the length or width if they are large.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Surface Floor or wall, Length 24 ft, Width 16 ft, Sheet size 4 × 8 ft, Waste 10%, Price per sheet $45.00 gives Sheets to buy 14, Sheets without waste 12, Cost $630.00.Source: Wikipedia, Plywood (the most commonly used sheets are 4 by 8 ft, 1,220 × 2,440 mm; 1,200 × 2,400 mm is a common metric size; 5 × 5 ft is common for Baltic birch), https://en.wikipedia.org/wiki/Plywood (retrieved 2026-10-03)
  2. Surface Pitched roof, Length 40 ft, Width 30 ft, Roof pitch, rise in 12 9, Sheet size 4 × 8 ft, Waste 0% gives Roof slope factor 1.25, Area to cover 1,500 ft², Sheets to buy 47.Source: Wikipedia, Plywood (the most commonly used sheets are 4 by 8 ft, 1,220 × 2,440 mm; 1,200 × 2,400 mm is a common metric size; 5 × 5 ft is common for Baltic birch), https://en.wikipedia.org/wiki/Plywood (retrieved 2026-10-03)
  3. Surface Floor or wall, Length 15.75 ft, Width 7.874 ft, Sheet size 1,200 × 2,400 mm, Waste 0% gives Sheets to buy 4, Sheets without waste 4.Source: Wikipedia, Plywood (the most commonly used sheets are 4 by 8 ft, 1,220 × 2,440 mm; 1,200 × 2,400 mm is a common metric size; 5 × 5 ft is common for Baltic birch), https://en.wikipedia.org/wiki/Plywood (retrieved 2026-10-03)
  4. Surface Pitched roof, Length 40 ft, Width 30 ft, Roof pitch, rise in 12 6, Sheet size 4 × 8 ft, Waste 10% gives Roof slope factor 1.118034, Sheets to buy 47.Source: Wikipedia, Plywood (the most commonly used sheets are 4 by 8 ft, 1,220 × 2,440 mm; 1,200 × 2,400 mm is a common metric size; 5 × 5 ft is common for Baltic birch), https://en.wikipedia.org/wiki/Plywood (retrieved 2026-10-03)

How it works

  • Roof slope factor = √(1 + (pitch ÷ 12)²) for a pitched roof, where pitch is the rise in inches per 12 in of run; 1 for a floor or wall.
  • Area to cover = length × width × slope factor.
  • Sheets without waste = area ÷ sheet area.
  • Sheets to buy = sheets without waste × (1 + waste ÷ 100), rounded up.
  • Cost = sheets to buy × the price per sheet, when you type a price.

Sheet sizes. 4 × 8 ft (32 ft²), 4 × 9 ft (36 ft²), 4 × 10 ft (40 ft²), 5 × 5 ft (25 ft²), 1,200 × 2,400 mm (2.88 m²), or a length and width you type.

Rules

Lengths, widths and a custom sheet’s sides are from 1 cm to 10 km; the pitch 0 to 48 in 12; waste 0 to 100%.

Output format

Sheets to buy is a whole number; sheets without waste shows to 2 decimals, the slope factor to 4, the area in ft² (US) or m² (Metric) to 2 decimals, and the cost in money. Typed sizes are read back as exact decimals; the slope factor is exact when it is a whole fraction (9/12 gives exactly 1.25) and a float otherwise; the count is rounded up once.

The answer reads: "Sheets of plywood to buy: [sheets], for [area]."

Worked examples by hand

A 24 × 16 ft subfloor, 4 × 8 sheets, 10% waste, $45 a sheet. 384 ft² ÷ 32 = 12 sheets; × 1.1 = 13.2, so 14 sheets; 14 × $45 = $630.

A 40 × 30 ft roof in plan at 9/12, no waste. Factor √(1 + 0.75²) = √1.5625 = 1.25. Area 1,200 × 1.25 = 1,500 ft²; ÷ 32 = 46.875, so 47 sheets.

A 4.8 × 2.4 m floor, 1,200 × 2,400 mm sheets, no waste. 11.52 m² ÷ 2.88 = 4 sheets exactly.

The same roof at 6/12 with 10% waste. Factor √1.25 = 1.1180; area 1,341.6 ft²; ÷ 32 = 41.93; × 1.1 = 46.12, so 47 sheets.

Other questions people ask

How many sheets of plywood do I need?

Divide the area by the area of one sheet, add waste for cuts, and round up. A 24 × 16 ft floor is 384 ft²; 384 ÷ 32 = 12 sheets of 4 × 8, or 14 with 10% waste.

How many square feet is a sheet of plywood?

A 4 × 8 ft sheet covers 32 ft². A 4 × 9 ft sheet covers 36 ft², a 4 × 10 ft sheet 40 ft², and a 5 × 5 ft sheet 25 ft². A metric 1,200 × 2,400 mm sheet covers 2.88 m².

How do I work out plywood for a roof?

Measure the roof from above (its plan, with overhangs) and multiply by the slope factor √(1 + (pitch ÷ 12)²). A 9/12 roof has a factor of 1.25, so a 40 × 30 ft plan is 1,500 ft² of roof deck, 46.9 sheets, so 47.

Does this work for OSB?

Yes. OSB is sold in the same sheet sizes as plywood, so the count is the same.

How much waste should I add?

About 10% covers cuts at edges and around openings for a simple floor or wall. Use more for a roof with hips and valleys or a room with many corners.

Should I take out windows and doors?

For wall sheathing, small openings are usually sheathed over and cut out, so leave them in. Take out large openings by shortening the length you type.